Commonly assigned U.S. Pat. No. 4,850,319 describes an Electronic Throttle Actuator for an internal combustion engine. One of the features of that patent is the inclusion of redundant torsion springs for biasing the throttle mechanism toward idle position so that each spring is capable by itself of returning the throttle mechanism to idle.
Since a throttle position sensor is another important component of an electronic engine throttle control, its replication in the system may also be desirable. For example, if two throttle position sensors that have substantially identical electrical characteristics are coupled in substantially the same manner with the throttle mechanism, they should at all times give substantially identical electrical signals so that a discrepancy between signals will indicate a need to inspect the system for the cause or causes of the discrepancy.
The present invention has been made in consequence of the applicants' recognition that correspondence between the throttle position sensors' signals is not in all circumstances necessarily a complete guarantee that both are providing signals that are true of current throttle position. For example, the occurrence of certain forms of short circuits in one of the two sensors will load down the power supply to the sensors in such a way that each sensor will give about the same signal as the other, but neither signal will correctly represent throttle position.
The present invention provides means to avoid the occurrence of such a situation. In the disclosed embodiment of the invention, both throttle position sensors are electrically energized from a common power supply, but an isolation circuit is provided between each sensor and the common power supply such that the occurrence of a short in one of the two sensors that would otherwise cause the sensors to give substantially identical, but inaccurate, signals will cause a discrepancy between the signals indicative of a need to investigate the cause or causes of the discrepancy. In this way, it becomes possible to promptly initiate corrective action toward identifying and replacing a shorted sensor. Advantageously, the isolation circuits can be of quite simple form, RC circuits being very satisfactory.
The foregoing features, along with further advantages and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by a drawing. The drawing illustrates a presently preferred embodiment of the invention according to the best mode contemplated at this time for putting the invention into practice.